Projectile guide mechanism

ABSTRACT

A guide mechanism for a projectile (2) which is intended to be fired from a barrel (3) with the aid of propellant gases. The projectile comprises a plurality of elongated fins (5) which are journalled at one end thereof and which are arranged to occupy a folded position during passage of the projectile through the barrel. The fins are subjected to a fin-extending force with the aid of a piston (7) which is arranged for movement in a housing (6) in the guide mechanism. The guide mechanism also incorporates a channel means (10) through which during a pressure increase phase of the propellant gases in the barrel the gases are passed to a chamber (9) located on one side of the piston and build-up a piston working pressure (p) in said chamber. The channel means (10) has arranged therein a valve (11) which is operative in throttling the channel means during a pressure reduction phase of the propellant gases. This pressure reduction phase can be dimensioned to commence before the guide mechanism reaches the muzzle of the barrel.

TECHNICAL FIELD

The present invention relates to a guide mechanism for projectiles ofthe kind which are fired from a barrel with the aid of a propellantcharge, the guide mechanism including a plurality of elongated finswhich are journalled at one end thereof and which are held in a foldedposition during passage of the projectile through the barrel and arearranged to be extended by means of a finextending force delivered by apiston arranged for movement in a guide-mechanism housing while indogging engagement with the fins, and which mechanism further compriseschannel means through which propellant gases are delivered to a chamberlocated on one side of the piston during a pressure increase phase ofthe propellant gases in the barrel.

BACKGROUND PRIOR ART

Guide mechanisms of the aforesaid kind are known to the art from, forexample, German Patent Specification DE No. 960 882. It has been found,however, that with this known mechanism the fins are often extended muchtoo slowly, resulting in insufficient muzzle stability of theprojectile. The tail of the projectile is namely still influenced by thepressure exerted by the propellant gases (powder gases) even when theguide surfaces of the projectile have left the muzzle of the barrel, anduneven loads on the fins can therewith cause pronounced wobble or yaw ofthe projectile in the vicinity of said muzzle, resulting in impairedexternal ballistics and impaired precision. This problem is particularlydifficult to overcome in the case of dart shaped or sweepbackprojectiles.

DISCLOSURE OF THE INVENTION

Consequently, the object of the invention is to provide a guidemechanism of the aforementioned kind with which the fins are extendedmore rapidly than with guide mechanisms known hitherto. The inventionrelates particularly, but not exclusively, to the provision of such aguide mechanism in which the fin-extending force is able to act on thefins before the projectile has reached the nozzle of the barrel, therebyenabling the fins to stabilize the projectile during the actual passageof the projectile through the barrel.

This object is achieved with a guide mechanism constructed in accordancewith the invention and having the characteristic features set forth inthe characterizing clause of claim 1.

Further developments of the invention are disclosed in the dependingclaims.

As a result of throttling the channel means in the guide mechanismduring the pressure reduction stage, the level of the working pressureis increased and the time taken to evacuate the chamber prolonged. Thiscauses the fins to be extended much more quickly than was previously thecase, and makes possible, inter alia, the aforesaid earlyfin-stabilization of the projectile during its passage through thebarrel.

This latter possibility of particular importance when firing with modernlightweight barrels constructed in accordance with wound-glassfibretechniques. Such firing barrels have a large radial stretch, i.e. largeclearance, and hence poor precision can be expected. This problem cannow be solved in accordance with the invention due to the fact that whennecessary (primarily, but not exclusively, in the case of dart-likeprojectiles) the fins can be caused to extend outwardly prior to theguide mechanism reaching the muzzle of the barrel. The fins are therebyurged against the barrel wall and stabilize the rear part of theprojectile during its travel through the barrel.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in more detail with reference to theaccompanying drawing, which schematically illustrates a preferredembodiment of the invention.

FIG. 1 illustrates the guide mechanism during the pressure increasephase, whereas

FIG. 2 illustrates the guide mechanism during the pressure reductionphase.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates the rear section 1 of a projectile 2, for example aconventional dart-shaped or sweepback projectile. The projectile 2 ismounted in a conventional manner in a cartridge or shell (not shown)intended for insertion to a loaded position in the preferably rifledbarrel 3 of a weapon (not shown in detail), for example an anti-tankrifle. The rear section 1 of the projectile is provided with a guidingand stabilizing mechanism in the form of a plurality of elongated fins 5which are journalled at one end thereof on a respective journal 4 andwhich, together with the rear section 1 of the projectile, are arrangedto be encased in the cartridge or shell, with the fins 5 lying looselyagainst the rear section 1, in the absence of separate securing devices.The fins 5 remain in their folded state during passage of the projectilethrough the barrel. The journals 4 are fitted to flanges or lips 4aprojecting outwardly from the rear section 1 of the projectile 2. Eachof the fins 5 presents a knee 5a which is intended to be held pressedagainst the wall of the barrel 3 during a pressure reduction phase ofthe propellant gases. The knee 5a reduces the length of the lever arm ofthe fin-extending force, to the distance between the knee 5a and theassociated journal 4. Each fin 5 also has arranged in its rearward end ashoulder 5b, the function of which will be described hereinafter.

The rear section 1 of the projectile 2 has formed therein a recess 6which forms a housing in which a sleeve-shaped piston 7 is arranged formovement in the direction of the longitudinal axis of the projectile.The rear end of the piston, as seen in the firing direction of theprojectile (marked by the arrow on the far left of the Figures), isfully open, whereas the forward end of the piston 7 is closed by a wall8. The interior of the sleeve-shaped piston 7 therewith forms a chamber9 in which a piston-working pressure p is able to act on the rear wallof the recess or cavity 6.

The wall 8 has provided therein a throughpassing aperture 10,hereinafter referred to as the channel means, in which a valve in theform of a plunger 11 can move in the direction of the longitudinal axisof the projectile. Arranged in the rear part of the valve 11 is a radialor transverse channel 12 which joins at its centre a channel 13 whichextends in the direction of the longitudinal axis of the valve 11 anddeparts from the forward end thereof. Axial movement of the valve 11 islimited by stop heads 14 and 15 located on a respective end of thevalve.

In the inactive position, the shoulder 5b of the respective fins abutsthe wall 8 of the piston 7, so that a fin-extending force can be exertedon the fins when the piston is caused to move forwards from the positionshown in FIG. 1.

The recess 6 is provided with elongated openings 16 for accommodatingthe shoulders 5b of respective fins 5, so that the shoulders are able tomove as the fins are extended.

The projectile is arranged to be fired from a cartridge or shell, notshown, in a conventional manner, with the aid of a propellant in theform of a powder charge. FIG. 1 illustrates the position in which theprojectile 2 has left the cartridge and commenced its passage throughthe barrel 1. In this stage the fins are still folded-in against therear of section 1 of the projectile. The valve 11 is pressed rearwardlyas a result of the acceleration of the projectile, until the stop head14 is pressed against the wall 8 of the piston 7, as illustrated inFIG. 1. Propellant gases deriving from the propellant charge therewithpenetrate through the openings 16 (c.f. the arrows in FIG. 1) and enterthe space in the housing 6 in front of the valve 7, from where they passthrough the channels 13 and 12 to the piston chamber 9, where thepressure p of the bases is built-up. This takes place during a pressureincrease phase of the propellant gases. Then the pressure of thepropellant gases begins to decrease, i.e. the so-called pressurereduction phase, which according to the invention should be arranged totake place before the fins have reached the muzzle of the barrel 3, thegas pressure in the recess 6 forwardly of the piston 7 begins todecrease, due to the diminishing pressure of the propellant gases.Consequently, the valve 11 is moved forward under the influence of theworking pressure p in the chamber 9, to the position shown in FIG. 2,where the radial channel is blocked by the walls of the channel means 10in the wall 8. The channel means 10 is now throttled, i.e. the valve 11occupies a closed position. The time taken to close the valve 11 isdetermined by the acceleration of the projectile, by the diameter of theaperture 10, and by the pressure p in the chamber 9. The pressure p isdetermined, in turn, by the gas pressure generated by the powder charge,the diameter of the channel 13, and the volume of the chamber 9. Thevalve closing time can thus be chosen within relatively wide limits.

When the valve 11 closes due to a decrease in pressure in front of thepiston 7, the piston will thus strive to move forward, i.e. to the leftin FIG. 2, under the influence of the working pressure p, and therewithpress against the shoulders 5b of respective fins and brings afin-extending force to bear thereon. The fins 5 are therewith urgedagainst the wall of the barrel 3 through the agency of the knees 5a ofrespective fins, so as to achieve the desired guidance of the rearsection of the projectile during its passage through the barrel. As soonas the fins have reached the muzzle of the barrel, the fins are openedout to a fully extended position, and can be locked firmly in thisposition in a conventional manner, e.g. by wedging the fins with wedgingmeans in accordance with Swedish Patent Specification SE No. 154 665.

Although the aforementioned dimensional parameters are preferablyselected so that the fins are subjected to a fin-extending force priorto the fins reaching the muzzle of the barrel, these dimensionalparameters may alternatively be selected so that outward extension ofthe fins commences at the same time as the fins reach the muzzle. Due tothe fact that the valve 11 prevents gas from leaking from the pistonchamber 9, a maximum piston pressure is attained for extension of thefins, and hence the fins will be extended much more quickly than withknown guide mechanisms. Tests have shown that when using a guidemechanism according to the invention, the fins are fully extended withina distance of only one meter after leaving the muzzle of the barrel, ata projectile velocity of about 300 m/s.

The structural components of the guide mechanism can be varied in manyways. The valve 11 may, for example, have the form of a conventionalnon-return valve. Furthermore, the wall 8 of the piston 7 may beimperforate and the channel means 10 arranged in the wall of the housing6 instead.

I claim:
 1. A guide mechanism for a projectile (2) which is intended tobe fired from a barrel (3) with the aid of propellant gases, comprisinga plurality of elongated fins (5) which are journalled at one endthereof and which are arranged to occupy a folded position duringpassage of the projectile through the barrel, and which fins aresubjected to a fin-extending force with the aid of a piston (7) which isarranged for movement in a housing (6) in the guide mechanism while indogging engagement with the fins, a valve (11) being mounted coaxiallywithin the piston and slideably therein, the valve being operative as aresult of initial setback forces on the projectile to open a channelmeans (10) in the valve, such that, during a pressure increase phase ofthe propellant gases in the barrel, said gases are passed through saidchannel means to a chamber (9) located on one side of the piston inorder to build-up a piston working pressure in said chamber, the valvebeing operative in throttling the channel means as a result of apressure reduction phase of the propellant gases.
 2. A guide mechanismaccording to claim 1, characterized in that the housing (6) is providedwith openings (16) through which, during the pressure increase phase,the propellant gases are also passed to a space located on the otherside of the piston (7), and through which evacuation of said spacecommences during the pressure reduction phase.
 3. A guide mechanismaccording to claim 1, characterized in that the pressure reduction phaseis dimensioned to commence prior to the guide mechanism reaching themuzzle of the barrel, such that said fin extending force begins to acton the fins before the projectile has reached said muzzle.
 4. A guidemechanism according to claim 3, characterized in that the fins (5)present a knee (5a) which when abutting the barrel wall (3) reduces amomentum arm of the fin-extending force.
 5. A guide mechanism accordingto claim 1, characterized in that the piston (7) is movable in thefiring direction of the projectile (2) under the influence of saidworking pressure.
 6. A guide mechanism according to claim 1,characterized in that the fins (5) are provided with respectiveshoulders (5b) which co-act with the piston (7).